Process for cross-linking silver halide gelatino emulsion layer containing non-diffusible compound having epoxide and isocyanate groups

ABSTRACT

PHOTOGRAPHIC GELATINE LAYERS HAVE TO BE HARDENED IN ORDER TO IMPROVE THE MECHANICAL PROPERTIES AND TO RAISE THE MELTING POINT OF THE LAYER. EXCELLENT HARDENING IS OBTAINED BY MEANS OF LOW MOLECULAR COMPOUNDS HAVING A HARDENY EPOXIDE AND A HARDENING ISOCYANATE GROUP.

United States Patent Office 3,729,318 Patented Apr. 24, 1973 3,729,318PROCESS FOR CROSS-LINKING SILVER HALIDE GELATINO EMULSION LAYERCONTAINING NON-DIFFUSIBLE COMPOUND HAVING EPOX- IDE AND ISOCYANATEGROUPS Wolfgang Himmelmann, Opladen, Peter Bergthaller,

Cologne, and Bernd Quiring and Kuno Wagner, Leverkusen, Germany,assiguors to Agfa-Gevaert Aktiengesellschaft, Leverkuseu, Germany NoDrawing. Filed July 21, 1971, Ser. No. 164,811 Claims priority,application Germany, July 25, 1970, P 20 36 998.6 Int. Cl. G030 1/30 US.Cl. 96--111 4 Claims ABSTRACT OF THE DISCLOSURE Photographic gelatinelayers have to be hardened in order to improve the mechanical propertiesand to raise the melting point of the layer. Excellent hardening isobtained by means of low molecular compounds having a hardeny epoxideand a hardening isocyanate group.

The invention relates to a process for hardening layers which containgelatin using a hardener which is fast to diffusion.

The irreversible cross-linking of the binder of photographic layers isof considerable importance because these layers are treated with variousaqueous baths in the course of processing and they must therefore behighly resistant to aqueous solutions, and particularly to alkalinesolutions. This is achieved by adding to the proteins which commonly areused to form the layer substances which are capable of undergoing across-linking reaction with the protein chains thus raising the meltingpoint of the proteins. This reaction, however, must not reduce thepermeability of the proteins to water and in many cases, e.g. in thesilver salt diffusion process, it is in fact desirable that the hardenedlayers should be capable of rapidly taking up a large quantity of waterin order to ensure rapid and complete processing.

Numerous compounds and types of compounds which may be used as hardenersfor proteins have already become known. The following are given asexamples:

Metal salts, such as salts of chromium, aluminium and zirconium;aldehydes and aldehyde compounds which contain halogen, e.g.formaldehydes, dialdehydes and mucochloric acid; 1,2- and 1,4-diketonessuch as cyclohexane-l,2-dione, quinones, chlorides of dibasic organicacids, dianhydrides of tetracarboxylic acids, and compounds whichcontain several reactive vinyl g-roups,' e.g. vinyl sulfones, andarylamides; compounds which have at least two heterocyclic rings whichare easily cleaved, e.g. ethylene oxide and ethylene imine,polyfunctional methane sulfonic acid esters, bis-a-chloroacylamidocompounds and heterocyclic compounds which have active halogen atoms,e.g. halogeno-1,3,5-triazine compounds.

These hardeners are low molecular weight compounds. Some of them arephotographically active and therefore cannot be used for certainphotographic emulsions. Others, such as the metal salts, increase thebrittleness of the layers. Dialdehydes and diketones discolor the layersin various ways and are therefore unusable. Furthermore, acid chloridesand acid anhydrides in many cases alter the pH of the casting solutionsso that the pH would have to be readjusted with alkali, which isundesirable or may be impossible because it would impair otherphotographic properties. It is also known that many hardeners causefogging or a reduction in the sensitivity of the emulsion afterprolonged storage.

Other hardeners again have the disadvantage that the hardening processstarts only after some time in storage so that the properties of thelayers undergo uncontrollable changes. Lastly, all hardeners which arenonditfusion-fast have the disadvantage that when used in multilayeredmaterials it is difficult to confine their activity to a particularlayer.

High molecular weight hardeners have also been described, e.g. periodicoxidation products of starch, and plant gums such as tragacanth, gumarabic, alginic acid, pectins and xylans. These compounds have, however,the disadvantage that they have only a low hardening equivalent. Alginicacid esters and maleic acid half esters of high molecular weightalcohols such as polyvinyl alcohol have similar disadvantages.

Lastly, macromolecular polymerization products of acrolein have alsobeen proposed as hardeners, but they can only be used in the form oftheir water-soluble bisulfite addition compounds. This is a disadvantagebecause after preparing the polyacrolein it is necessary to carry out asecond operation to obtain the bisulfite addition compound, and theremoval of excess sulfurous acid or sulfite can only be achieved bycomplicated operations.

Now, as before, there is a need for ditfusion-fast hardeners which canbe used for producing photographic materials which contain an unhardenedlayer adjacent to a highly cross-linked layer. Such systems are veryimportant for so-called stripping films. Hardeners which are notdiffusion-fast naturally cannot be used for these films because thehardener become distributed throughout the whole stack of layers and allthe layers would be crosslinked. Low molecular weight hardeners could inprinciple be rendered diffusion-fast by known methods. Thus, forexample, longer al kyl radicals having more than 10 carbon atoms couldbe introduced. This method, however, generally leads to complete orpartial loss of the hardening activity of the hardeners. Although highmolecular weight hardeners are diffusion-fast, they have various otherdisadvantages, as already mentioned above. For example, the viscosity oftheir aqueous solutions is relatively high, which makes processing moredifiicult. Moreover, it is diflicult to free high molecular weightcompounds from unwanted impurities.

It is among the objects of the invention to provide low molecular weightdiffusion-fast hardeners for protein layers, by means of which thehardening process can be confined to one layer within a multilayeredphotographic material.

A process for hardening photographic gelatin layers by the addition oflow molecular weight hardeners has now been found in Which the hardenersused are compounds which contain an isocyanate group and an epoxidegroup.

The hardening compounds correspond, for example, to the follomingformula:

wherein Z represents a bivalent organic linking member, preferably abranched or unbranched, saturated or ethylenically unsaturated aliphaticradical containing up to 10 carbon atoms, arylene, especially phenylene,or cycloal-kylene, preferably cyclohexylene, which may be interrupted byether (O), carbamoyl (CONH) or urethane (OCONH-) groups.

More particularly suitable are compounds of the following formula:

wherein n represents the integer 1, 2 or 3, preferably 1 or 2, each of Xand X represents a bivalent hydrocarbon group with up to 18 carbonatoms, preferably with 2 to carbon atoms. More particularly X and Xrepresent a bivalent straight-chain or branched aliphatic group, whichmay be saturated or olefinically unsaturated, a bivalent cycloaliphaticgroup such as cyclohexylene, a bivalent aromatic group such as phenyleneor naphthylene. Also included are mixed hydrocarbon groups, for examplecombinations of aliphatic groups with aromatic or cycloaliphatic groupssuch as tolylene or xylylene or methylenecyclohexylene. Particularlypreferred are compounds in which X stands for an aliphatic group havingup to 10 carbon atoms.

The compounds for use according to the invention are characterized bythe isocyanate group and the epoxide ring. Both groups react with aminogroups of the protein binder, e.g. gelatin, but the isocyanate groupreacts much more rapidly than the epoxide group, in fact it reactsimmediately when these compounds are added to the solu tion of protein.The hardener is thus combined in a diffusion-fast manner with the filmforming agent. The epoxide group which reacts much more slowly reactsonly after the layer has been produced, in the course of drying orstorage of the photographic material. Herein lies the advantage of thecompounds used according to the invention. The cross-linking agent isfixed by the one reactive group, but the viscosity of the proteinsolution is not increased. The compounds therefore behave quitedifferently from those which contain two isocyanate groups or twoepoxide groups. Those which contain two isocyanate groups react sorapidly in aqueous solution that cross-linking and a high increase inthe viscosity is even observed in the casting solutions. Compounds whichhave two epoxide groups react only slowly in the course of drying orstorage and they are therefore not present in a diffusion-fast form inthe layers.

The two functional groups of the hardeners according to this inventionare connected together by the linking member Z in Formula I. The linkingmember due to its non-critical nature, can of course be of anystructure, and accordingly the hydrocarbon groups can be substituted,for example, with alkyl which would constitute an aliphatic hydrocarbonside chain, or with alkoxy or halogen, especially chlorine. However thesubstituents should not impair the reaction of the epoxide or isocyanategroups with gelatin.

Compounds of the following formulae have proved to be especiallysuitable:

CHz-NCO CH3 i C l NCO COMPOUND 4 25 g. ofdipheny1methane-4,4-diisocyanate (Desmodur- 44) (0.1 mol) are dissolvedin m1. of xylene and heated to 100 C. and 7.4 g. of glycidol (0.1 mol)are added at this temperature. The reaction mixture is cooled and thesupernatant layer is decanted from the oil which has separated and theoil is boiled several times with petroleum ether. Yield about 30 g.

COMPOUND 52.2 g. (0.3 mol) of tolylene-2,4-diisocyanate (0.3 mol) in 150ml. of clean petrol ether are heated to 100 C., 100 mg. of1,2,4-triazole are added as a catalyst, and 22.2 g. of glycidol (0.3mol) are the introduced dropwise with stirring. The supernatant layer isdecanted while still hot from the bis-glycidyl urethane which hasseparated. This is then left to get cold and the crystallized product isfiltered off. Yield 40-50 g.

COMPOUND 7 67 g. of isophorene diisocyanate (0.3 mol) are heated to 100C., 22.2 g. of glycidol (0.3 mol) are added drop- Wise with stirring,the reaction mixture is left to get cold and the resulting viscous massis boiled several times with petroleum ether. Yield 70 g.

COMPOUND 9 (a) A solution of 33.6 g. of hexamethylenediisocyanate in 20g. of absolute benzene is heated to 80 C. and 7 g. of glycidol are addeddropWise with stirring. The solution is then heated for one hour at 80C. and filtered, and benzene and excess diisocyanate are removed undervacuum. A thick oil remains. Yield 35 g.

(b) 50.4 g. of hexamethylene diisocyanate (0.3 mol) are heated to 100C., 22.2 g. of glycidol (0.3 mol) are added dropwise with stirring, thereaction mixture is left to cool and the viscous oil is boiled severaltimes With petroleum ether. Yield 60 g.

COMPOUND 10 17.4 g. (0.1 mol) of commercial tolylene diisocyanate(approximately 80% 2,4- and 2,6-tolylene diisocyanate) are heated to 100C., 11.8 g. of ethylene glycol monoglycidyl ether are added dropwisewith stirring, the reaction mixture is left to cool after minutes andthe oil is extracted several times With petroleum ether. Yield: 30 g. ofan oil which contains substantial quantities of petroleum ether.

For the preparation of compounds for use according to the invention seealso German Oifenlegungsschrift No. 1,901,024 or US. application Ser.No. 843.

The term photographic layers includes quite generally any layers usedfor photographic materials, e.g. light sensitive silver halide emulsionlayers, protective layers, filter layers, antihalation layers, backinglayers or photographic auxiliary layers in general.

The effect of the compounds used according to the invention is notimpaired by the usual photographic additives and the hardeners accordingto the invention are also inert to photographicaly active substancessuch as color couplers, stabilizers and sensitizers. Also, they have noinfluence on the light sensitive silver halide emulsions.

The compounds are preferably used in the form of their solutions inaprotic solvents in quantities of 0.5 to 8%, preferably 1 to 5% (basedon the dry weight of gelatin). They are added before the gelatinsolutions are cast and preferably before digestion. The solutions arethen digested for at least /2 hour at to C. to ensure that theisocyanate groups have undergone complete reaction. This is essential toensure that the hardener is fixed in a diffusion-fast form. The layerbinder may contain other water-soluble high molecular Weight compoundsin addition to gelatin, e.g. polyvinyl alcohol, polyvinyl pyrrolidone,polyethylene oxide and polyacrylamide and latices of water-insolublehigh molecular weight compounds such as polyethyl acrylate,polybutylcryltae and other copolymers which serve as plasticizers or asadditives which increase the covering power of silver. Casting may befollowed by a prolonged period of drying before a new layer is applied.The technical advance provided by the application of the compoundsaccording to the invention consists in the fact that hardening isstrictly confined to layer to which the hardener has been added. Whenbuilding up an assembly of layers, there is no difiiculty in following astrongly hardened layer with a less hardened or unhardened layer. Whenusing conventional hardeners, the preparation of multilayered assembliesof this kind can generally only be achieved if certain precautions aretaken. If, for example, a layer of unhardened gelatin which can bewashed off at 36 C. is to be cast onto a layer I which has been hardenedwith formalin, the excess formalin must either be removed from layer Iby storing the layer or tempering it at elevated tempertaures or morepreferably an intermediate layer which binds the formalin must be placedbetween layers I and II.

The melting point of the layers is determined as follows: Half of thelayer which has been cast on a support is dipped in cold water which iscontinuously heated by 5 C. per minute up to C. The temperature at whichthe layer runs off the support (formation of streaks) is taken as themelting point. In other tests, the layers which had been hardened inaccordance with the invention weie first treated for 5 minutes with a 5%aqueous sodium carbonate solution and the melting points were thendetermined both immediately after drying and after the layers had beenstored as indicated above. Under the conditions at which the measurementare carried out, pure gelatin layers which contain no hardener in nocase showed an increase in melting point.

Example 1 5 ml. of a 5% aqueous saponin solution are added as wettingagent to cc. of a 10% aqueous gelatin solution and the compounds areadded in each case in amounts of 2% based on the gelatin content. Thecompounds are dissolved in ethyl acetate and dispersed in the gelatin.The pH of the solution is adjusted to 6.2. The casting solutions arepoured on a previously prepared cellulose triacetate support. Afterdrying, the layers (layer I) are stored for 36 hours at 57% C. and 34%relative humidity. After determination of the melting point, the castlayer is covered with a conventional silver halide gelatin emulsionwithout hardener, which emulsion contains 45 g. of silver halide and 60g. of gelatin per kg. The melting point of the emulsion layer (layer II)is determined after storing for 36 hours at 57 C. and 34% relativehumdity.

The figures above show that in contrast to the triazine hardeners, thecompound according to the invention are diffusion-fast, and hardening isin each case confined to the layer to which the hardener has been added.

Example 2 1%, 2% and 5%, respectively, of the compounds according to theinvention dissolved in ethyl acetate solution (percentage content basedon the gelatin) were added in an emulsified form to 1 kg. of a silverhalide gelatin emulsion of the type conventionally used for black andwhite material containing per kg. 80 g. of gelatin. The solutions areleft to stand for /2 hour at 36 C. and then cast on a baryta-coatedpaper support after the addition TABLE II Melting point of the layer in0.

Swelling Condition I Condition II in percent Compound 1:

l00 495 2 10100 400 Compound 2:

1% 42 45 2% 540 Compound 3:

1% 41 44 2% 590 Compound 4 360 2% 280 Compound 7:

0 50 5100 590 2% 2l00 10100 550 Compound 5:

1% 62 10100 -1 520 2% 10100 10100 390 Compound 9 42 10l00 2% 10100 1or00430 Compound 10:

1% 38 3100 490 2% 50 l0'l00 420 Compound 11:

17 465 27 390 Compound 1 1% 50 515 2% 2l00 10l00 360 Compound 13:

1 10100" means that the melting point of gelatin is above 100 C. and thea yer dissolves 013 only after 10 minutes boiling in water.

The table shows that the compounds according to the invention areefficient hardeners. They do not influence the photographic propertiesof the emulsion.

Swelling of the layers is determined gravimetrically after 10 minutestreatment of the layers in distilled water at 22 C. and it is indicatedin percent.

Example 3 3 g. of Compound 5 and 3 g. of Compound 9, respec tively, areadded to 1 kg. of a silver chlorobromide emulsion which is ready forcasting and which contains g. of gelatin, silver halides in an amountwhich corresponds 50 to 38 g. of silver nitrate and 18 g. ofl-hydroxy-4-sulfo- N-octadecyl-2-naphthamide as cyan-forming coupler.The emulsions were cast on a layer support of triacetylcellulose.Determination of the melting points of the layers and of the amount ofswelling were carried out after stor- 5 ing the material for 36 hours at57 C. and 34% relative humidity.

The photographic properties are not affected and the color shade of thedye is not altered.

Example 4 2% of Compound 7 (based on gelatin) are added to a 6% aqueousgelatin solution. The mixture is digested for /2 hour at 40 C. and it iscast on a previously prepared cellulose acetate support after theaddition of a Wetting agent. The layer is dried and kept for 36 hours at34% relative humidity at 57 C. A layer of gelatin which does not containhardener is then cast on the first layer. After drying, a silver halidegelatin emulsion to which 2% of Compound 7 have been added and which hasalso been digested for /2 hour at 40 C. is applied. After this has beenkept at 34% relative humidity and 57 C. for 36 hours, the melting pointof the upper and lower layer has risen to C. The melting point of themiddle layer is 42 C., which proves that the hardener is fast todiffusion.

We claim:

1. In a process for the production of a photographic light sensitiveelement having a plurality of layers including at least one silverhalide gelatino emulsion onto a layer support and drying, theimprovement consisting or casting a silver halide gelatino emulsioncontaining an effective amount of a non-diffusible compound having thefollowing formula:

wherein Z represents a bivalent, saturated or ethylenically unsaturatedaliphatic radical containing up to 10 carbon atoms, or arylene, dryingthe cast layer and cross-linking said compound in the dried silverhalide gelatino emul sion to yield a hardened layer.

2. The process of claim 1, wherein the hardening agent has the formulawherein n represents 1 or 2 and each of X and X represents a bivalentstraight-chain or branched aliphatic group, which may be saturated orolefinically unsaturated, or a bivalent cycloaliphatic group.

3. The process of claim 2, wherein X is an alkylene group having up to10 carbon atoms and X is (1) an alkylene group having up to 10 carbonatoms, (2) a bi valent cycloaliphatic group, (3) a phenylene group or(4) a bridge member containing alkylene and phenylene or alkylene and abivalent cycloaliphatic group.

4. A photographic light sensitive element having a plurality of layersincluding at least one sliver halide gelatino emulsion layer containingan effect amount non-diffusible compound having the following formula:

CHzCI -ICH2OZNCO wherein Z represents a bivalent, saturated orethylenically unsaturated aliphatic radical containing up to 10 carbonatoms, or arylene, said compound being cross-linkable in the driedsilver halide gelatino emulsion to yield a hardened layer.

References Cited UNITED STATES PATENTS 3,220,864 11/1965 Kenyon et al.96lll X 3,047,394 7/1962 Allen et al. 96l11 3,551,159 12/1970 Froehlich96-111 3,103,437 9/1963 Henn et al 96l11 NORMAN G. TORCHIN, PrimaryExaminer W. W. H. LOWIE, Assistant Examiner UNITED STATES PATENT OFFICECETEFICATE OF CORRECTION Patent No. 729315 Dated April 24. 1973Inventor(s) 'm] m,ann at al It is certified that: error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below: Column 1, line 21, "hardeny" should readhardening Column 1, line 52, "arylamides" should read acrylamides Column2, line 29, "hardener" should read hardeners Column 5, line 8, "the"should read then Column 5, line 71, "p-olybutylcryltae" should readpolybutylacrylate I Column 6, line 3, before "layer" insert the Column6, line 13, "tempertaures" should read temperatures Column 8, lines 16and '17, after "emulsion" insert layer by casting the gelatinoqemulsionafter "consisting" the word "or" should read of Signed and Sealed this20th day of November 1973'.

(SEAL) Attest:

EDWARD M.FI.ETCHER,JR. RENE D. TEGTl [EYER Attesting Officer 7 ActingCommissioner of Patents FORM PO-105O (10-69) US COMM-DC 60376-P69 u.s.GOVERNMENT Pmm'mc QFFICE I969 0-366-334,

